This invention relates to a drive shaft adapted for use in driving rolls of rolling mills and the like, and more particularly, to a drive shaft whose two tubular shafts are telescopically coupled together so as to transmit torque and to slide axially with an attached structure of a coiled spring acting to bias the two axially opposed tubular shafts.
A conventional drive shaft of the above type is disclosed in FIG. 4 of Japanese Utility Model Publication No. 55-16188. This drive shaft is configured such that a tubular shaft made integral with a first joint member is telescopically spline-fitted/coupled with another tubular shaft made integral with a second joint member and a coiled spring is provided inside the inner tubular shaft in the spline-fitted section. With the drive shaft thus configured, torque is transmitted from the first joint member to the second joint member via the spline-fitted portions of the two tubular shafts. To accommodate a variation in the distance between the first joint member and the second joint member during torque transmission, the tubular shafts are made axially slidable. The coiled spring is wound around a positioning guide bar provided inside the inner tubular shaft so that its outer peripheral surface faces the inner peripheral surface of the inner tubular shaft. Both ends of the coiled spring are held in contact with the respective base portions of the two tubular shafts so that the two tubular shafts are biased in axial opposition with the result that the two tubular shafts are stably retained in place. Since it is difficult to make the coiled spring in the form of one long element, two spring segments are used to form the coiled spring and a spacer ring is interposed between them.
In the foregoing drive shaft wherein the coiled spring is guided by the inner peripheral surface of the inner tubular shaft and the outer peripheral surface of the guide bar, flexure arises on the coiled spring during rotational motion because of the presence of a radial gap in the guide section. Thus, the coiled spring severely collides with the tubular shaft and/or the guide bar, resulting in a problem of significant noise and/or vibration being generated.
U.S. Pat. No. 4,112,710 and U.S. Pat. No. 4,136,532 also disclose drive shafts including coiled springs. That is, U.S. Pat. No. 4,112,710 teaches a coiled spring which is made of two spring segments connected together and disposed in conjunction with a guide bar as is the case of the abovementioned prior art. As a result, the coiled spring undergoes flexure during rotational motion and collides with a tubular shaft, resulting in a problem of significant noise and/or vibration being generated. U.S. Pat. No. 4,136,532 teaches one coiled spring of moderate length which is disposed around a tube and guided thereby. As a result, the coiled spring undergoes flexure during rotational motion and collides with a tubular shaft and the tube, resulting in a problem of significant noise and/or vibration being generated.